Telephone system



No. 624,881. Patented May 9, I899. D. MAcL. THERRELL.

TELEPHONE SYSTEM.

(Application filed. Apr. 6, 1897.)

(No Model.)

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, NITED STATES PATENT OFFICE.

DANIEL MACLAUCHLIN THERRELL, OF ATLANTA, GEORGIA.

TELEPHONE SYSTEM.

SPECIFICATION forming part of Letters Patent No. 624,881, dated May 9, 1899.

Application filed April 5, 1897. Serial No. 630,838; (No model.) i

To aZZ whom it may concern.-

Be it known that I, DANIEL MAOLAUOHLIN THERRELL, a citizen of theUnited States of America, and a resident of Atlanta, in the county of Fulton and State of Georgia, have made a certain new and useful Improvement in Telephone Systems; and I do hereby declare the following to be a full, clear, and exact description of the invention, reference being had to the accompanying drawing, and to letters and figures of reference marked thereon,which forms a part of this specification.

The accompanying drawing will represent the invention in conventional diagram.

The objects of this invention are, first, to

increase the power of the transmitter in a repeater system,enablin git to reach over greater distances, and, second, to provide an actually automatic and reciprocal repeater capable of furnishing additional that is, greater than the original impressionenergy of the same phase and undulations as the original to the main line, thus relaying automatically and reciprocally the voice-currents from either end of the line to the other.

This is accomplished as follows: First, in the transmitter shown at A and at B, the same figure, a is a microphonic carbon transmitter connected in local circuit 1 with the local battery Z), which local circuit includes the primary of the induction-coil c, as shown. The secondary of this induction-coil instead of being connected into the main line, as usual, is led to 2 and 3, where it divides into two short circuits 4 and 5 of equal resistance. In each of these derived short circuits there is an electromagnet d and e, respectively, so arranged as to have for their armatures the diaphragms of other microphonic carbon transmitters connected up with local-battery circuits 6 and '7, as shown, which local-battery circuits include the primaries of the two induction-coils f and g, which coils have their secondaries joined at each end and connected to the main-line terminals in multiple at 8 and 9. Now it will be seen that when the voice impinges upon the diaphragm of the transmitter a the diaphragm is set into vibrations corresponding to the vibration of the voice. Such vibration, as is Well known, by varying the pressure between the carbon and the diaphragm produces a variation in the current sent, through such carbon contact corresponding to the variation of the tones of the voice. This current, becoming impressed with the same wave form or undulation as the voice, in circulating in short circuit through the primary of the inductioncoil 0 induces a corresponding voice-current in the secondary thereof. This voice-current of the secondary upon reaching the points 2 and 3 divides equally between the two short circuits at and 5 of equal resistance and com taining,.respectiv'ely, electrom agnets d and e of like resistance. Therefore each of the said electromagnets receives exactly the same voice-current of the same Wave form and intensity in equal phase, strength, and. time. Such voice -currents, passing through these electromagnets in varying intensity corresponding to the vibrations of the voice, produce variations in the magnetic flux of the said magnets corresponding to the original vibrations of the voice. This varying flux acts upon the diaphragm of each of the carbon transmitters h and i in the same way at the same instant, so that the two are always in absolute synchronism. The diaphragms thus set into vibration corresponding tothe original voice vary the resistance in their local-battery circuits 6 and 7, giving the current in each the same wave form as the original voice-current. These battery-currents, flow ing through the primaries of the induction coils) and g,- induce similar currents in the secondaries of the two, which, flowing in the same direction, join at 8 or 9 in multiple and go to the main line 10, with the cumulative current of the two secondaries, but both of absolutely the same wave form and the same.

Wave characteristics in every particular. Thus is accomplished the increase of current upon the main line without any lapse or partial coincidence of the high and low intensities or the injurious efiects of heating the transmitter-electrodes, and thereby affecting the voice-currents. Of course this current may be increased by increasing the number of transmitters and coils placed in multiple synchronism between the main-line terminals 8 and 9. For instance, the secondary derived circuits, with their magnet-diaphragms, batteries, and coils, might be increased to four, thus increasing the main-line current fourfold that of one set.

The same principles enter into the operation of the telephonic repeater shown at C. To describe the operation thereof will be sufficient to a comprehensive understanding. As shown, the repeater is placed midway between the distant stations A and B. Now suppose the voice-currents transmitted from station A. Leaving the transmitter at 8 they come over the main line 10 to the repeatingstation 0. At 0 the main line is connected to the primary of the induction-coil j and also with the primary of the induction-coil 7c,

which coils are in series, as shown, both as regards primaries and secondaries. Between the two coils jand 76 in primary circuit at 11 there is a bridge connection 12 across to the other side of the main line 10. In this bridge connection there are placed in multiple two induction-coils Z and 1% upon the same principle as above described in the synchronous multiple transmitter. Each of these coils has for its primary a local-battery circuit 13 and 14, respective1y,a microphonic carbon transmitter 91 and 0, respectively, and synchronous electromagnets p and q in connection therewith, as shown, being connected upon circuits 15 and 16 of equal resistance, joined at 17 and 18 with electrical connections 19 and 20, respectively, to the secondaries of the induction-coils j and 7c, the other terminals of said secondary coils being connected through a differential galvanometer 7', which may be used for determining the balance of the line and indicating how much of the variable resistance at s or't is to be placed in circuit to approximately balance the main line 10..

The operation is as follows: The voice-curent from the transmitter at station A arrives over the main line 10 and passes through the primary of the coil j, dividing at 11, part going through the coil 7c in series with the primary coil j and part through the bridge connection 12 and the secondaries of the two coils Z and m in multiple and to the other side and back to station A. Now it will be seen that the main line current passing through the primaries of the coils j and thereby sets up an induced inverse current in their secondary windings, which are also in series. This secondary current in the secondary short circuit 19 upon reaching the point 17 divides equally between the two derived circuits 15 and 16 of equal resistance, and acting upon the electromagnets p and q therein reproduce the voice-currents in the transmitters n and 0, which set up fresh voicecurrents in their local-battery circuits 13 and 1.4. This transfers by induction the same voice-currents to the secondaries of the induction-coils Z and m, which have their termi nals connected in multiple in the bridge 12 between the main lines. The current from the synchronous secondaries of the coils Z and m, joining at 21, flows into the main line at 11 or 12, half going in each direction, providing the resistance of the two main lines is equal. If unequal, a variable rheostat resistance s and t is thrown into whicheverline is the lower until the differential galvanometer r indicates that the two are balanced. Thus the current that flows through the primary of the coil it onto the distant end B tends to set up an induced secondary in the opposite direction of the same value and at the same time that the current flowing back to the station A through the primary of the coil j sets up a secondary in an opposite direction to that of the coil is. As these two secondary currents are of equal value and in opposite directions, they meet at the dead point, which would be in the differential galvanometer r, and cancel each other, thus preventing any reaction upon the magnets 17 and got the repeater and eliminating all tendency to howl or buzz therein. In other words, the original main-line current from, say, station A in passing through, the primaries of the coils j and 70 (which are in series) in the same direction, sets up an induced current in the opposite direction in the secondaries of both coils, which are also in series, whereby their induced secondary currents are in the same direction and additive in volume, their total sum energizing and operating the electromagnets p and q of the repeating-transmitters and the batteries controlled thereby, through the secondaries of the coils Z and m reaches the point 11, and the current divides equally between the two main lines, passing through the primaries of the coils j and 7c in opposite directions, thereby setting up inverse currents in their secondaries, which, instead of beingin the same direction and additive as when the current passed through the primaries in the same direction in both as in the first instance, are now in opposite directions and, being of equal value, cancel each other and thus preventa reaction upon the electromagnets p and q.

Having thus described my invention, what I claim as new, and desire to secure by Letters Patent of the United States, is

1. A compound transmitter comprising a diaphragm, a variable resistance in operative relation to said diaphragm, a local circuit including said variable resistance, a source of energy in said local circuit, an induction=coil the primary of which is connected into the said local circuit, the secondary whereof is divided into two branches of equal resistance, variable-resistance repeating-transmitters in each branch of the said divided secondary circuit, local-battery circuits controlled by the said variable-resistance repeating-transmitters, induction-coils having their primaries in the said local-battery circuits and their secondaries connected into the main-line circuit in multiple, substantially as set forth.

2. In a compound telephone system, a repeater consisting of two receiving induction coils having their primaries in the main-line circuit and their secondaries connectedin series and divided or branched into two ormore short circuits, variable-resistance repeatingtransmitters in each branch circuit, induc tion-coils having their secondaries connected together in multiple and bridged across the main-line circuit between the two receiving induction-coils, and local-battery circuits including the primaries of said induction-coils and the variable-resistance portions of the said repeating-transinitters, substantially as set forth.

3. Means for automatically and reciprocally relayingvoice-currents orsound undulations,

from one line to another, consisting of induc tion-coils,the secondaries of which are bridged in multiple across the main lines, a source of energy and a variable-resistance device included in the primary circuit of each of the said induction-coils, separate circuits of equal resistance inductively derived from the main line, and a receiving-magnet included in each of said derived circuits and in operative rela- Q tion to said variable-resistance devices, substantially as set forth.

In testimony whereof I hereunto aflix my signature in presence of two witnesses.

D. MACLAUOHLIN THERRELL.

Witnesses:

ALBERT P. Wool), S. M. wool). 

